The present invention relates to electromechanical transducers which may, if necessary, also be pyroelectric obtained from polymer materials having a composite structure so as to obtain bimorph operation.
Polymer materials exist which can be given significant piezoelectric and pyroelectric properties as a result of certain treatments. This is the case, for example, with polyvinylidene fluoride (PVF.sub.2) and similar compounds such as polyvinyl chloride, polyvinyl fluoride, etc., as well as copolymers of these materials.
A device operating in bimorph manner can be obtained from a material of this type. For example a sheet of this material is taken and the two faces of electrodes are covered so as to form a capacitor. The bimorph element is obtained by associating with the said structure another sheet which can be inert from the standpoint of piezoelectric operation. When a voltage is applied between the two electrodes of the piezoelectric sheet it undergoes a normal stress and a tangential elongation.
Due to the mechanical coupling the other sheet is stretched at the interface. Finally the device bends, which represents a mechanical displacement by rotation much greater than that devolving from the constriction of the sheet.
However, there is only a relatively limited range of piezoelectric polymer materials and the piezoelectric properties only appear after a polarization treatment which can in certain cases be complicated. The constraint of a particular piezoelectric range often makes it impossible to choose materials having the desired mechanical properties.
The production of an electrostatic transducer from a random non-piezoelectric dielectric is also known. When exposed to an electrical field it undergoes an electrostatic pressure in the field direction, i.e. stretching in the perpendicular plane. However, this deformation is a quadratic effect of the electrical field and is therefore independent of the direction of said field.